Change the colours of a whole PDF in one go
The PDF Color Converter recolours every page of a PDF with one of five effects: grayscale, invert for dark-mode reading, warm sepia, high contrast for faint documents, and a simple RGB to CMYK conversion for print preparation. A live preview shows the effect on any page before you convert.
The colours are rewritten inside the file rather than painted over a picture of each page, so text stays sharp and selectable and the PDF keeps its links, bookmarks and form fields. For PDFs that cannot be rewritten — encrypted files, or pages built from unusual image formats — a rasterize option renders each page with the effect applied, and the report always tells you which method ran.
Everything is processed in your browser. Your document is never uploaded, which matters for contracts, study notes and client artwork alike.
How to change the colours of a PDF
- Drop a PDF onto the upload area or click to choose it.
- Choose a colour effect. The hint under the buttons explains what it does, and the preview on the right shows it on the current page — type another page number to check other pages.
- Adjust the options: the grayscale formula for Grayscale and High contrast, the strength for High contrast, or “Keep photos un-inverted” for Invert.
- Keep “Keep text & vectors” for the sharpest, smallest result, or pick “Rasterize pages” and a resolution if the first method leaves something unconverted.
- Press “Convert colours”, read the report, check the result preview and press “Download PDF”.
PDF Color Converter features
Five colour effects
Grayscale, invert, sepia, high contrast and RGB to CMYK, each applied consistently to text, shapes, gradients, images, spot colours and annotations.
Real dark mode
Invert adds a black page background and turns the default black ink white, so even text with no colour set comes out light on dark.
Photos can stay natural
With “Keep photos un-inverted”, only text and graphics are inverted while pictures keep their real colours.
K-only greys in CMYK
Black and grey become pure K (black ink) instead of a mix of four inks, which is what printers prefer for text.
Preview before converting
An instant on-page preview, then a result preview rendered from the converted file itself.
Honest fallback
If the colours cannot be rewritten, pages are rasterized with the same effect and the report says so.
What each colour effect does
Worked example for high contrast at the default strength of 2.2: a 30% grey (0.3) becomes (0.3 − 0.5) × 2.2 + 0.5 = 0.06, almost black, while a light 80% grey tint becomes 1.16, which is clipped to pure white.
| Effect | Formula | Good for |
|---|---|---|
| Grayscale | Grey = 0.2126 R + 0.7152 G + 0.0722 B (Rec. 709) or 0.299 / 0.587 / 0.114 (Rec. 601) | Black-and-white printing |
| Invert | Each channel becomes 1 − value; a black background is added | Reading at night, OLED screens |
| Sepia | R′ = 0.393 R + 0.769 G + 0.189 B, G′ = 0.349 R + 0.686 G + 0.168 B, B′ = 0.272 R + 0.534 G + 0.131 B | A vintage, warm look; softer screen reading |
| High contrast | Grey, then (grey − 0.5) × strength + 0.5, clipped to black and white | Faint photocopies, pale text, low vision |
| RGB → CMYK | K = 1 − max(R, G, B); C = (1 − R − K) ÷ (1 − K), likewise M and Y | Rough print preparation |
About the RGB to CMYK conversion
This conversion uses the textbook formula above. It is not ICC colour-managed: it knows nothing about your printer’s inks, paper or press, applies no total ink limit and does not simulate how vivid screen colours fall outside the printable gamut. Bright RGB blues and greens will usually print duller than they look on screen.
It is still useful for quick jobs — office printers, proofs, or a print shop that only accepts CMYK files — and it guarantees that greys and black text use black ink only. Colours that are already CMYK are left exactly as they are. For brochures, packaging and anything colour-critical, ask your print shop to convert with their press profile (for example Coated FOGRA39 in Europe or GRACoL in the US) and to show you a proof. Before sending artwork, check its trim and bleed with the PDF Bleed Checker and its structure with the PDF Validator.
Tips for dark-mode reading
- Invert is meant for screens. Printing an inverted PDF uses a great deal of toner, so convert a copy and keep the original for printing.
- Tick “Keep photos un-inverted” for textbooks and magazines so photographs do not look like negatives.
- Pages that already have a dark background become light after inverting — that is expected.
- For printing on a black-and-white printer, use PDF Grayscale; for crisp text scans, use PDF to Black and White.
PDF Color Converter FAQ
How do I invert the colours of a PDF?
Choose “Invert (dark mode)”, keep “Keep text & vectors” and press “Convert colours”. The PDF converter adds a black background, turns dark text light and inverts every colour. Download the result and open it in any PDF reader.
Can I convert a PDF from RGB to CMYK for printing?
Yes, choose “RGB → CMYK”. It converts every RGB colour and image with a standard formula and makes greys K-only. It is not colour-managed with an ICC profile, so for professional printing ask your print shop for a profile-based conversion.
Will my text still be selectable after changing colours?
Yes, with the default method. Only colour instructions change, so text remains real text. The rasterize method turns pages into images, and the report tells you when that happened.
Why do photos look like negatives after inverting?
Inverting flips every colour, including photographs. Tick “Keep photos un-inverted” to leave images untouched while text and graphics are inverted.
What does high contrast do to a PDF?
It converts the page to grey and stretches the tones around the middle, so faint text becomes darker and light tinted backgrounds become white. Choose a stronger setting for very pale photocopies.
Is my PDF uploaded to a server?
No. The colour conversion runs entirely in your browser and the file never leaves your device.